With the increasing spread of the Internet, for both commercial and private users, the number of installed DSL lines is also increasing. Consequently, power consumption, in both the lines and in corresponding transmitting and receiving units, is becoming ever greater. In switching centres, in particular, in which many such DSL lines converge, heat build-up and power consumption are so great that there is a need for energy-saving options.
The so-called ADSL2 (“Asymmetric Digital Subscriber Line”) Standard defined a so-called “low-power mode”, i.e., an energy-saving transmission mode. This mode is used when it is detected that only relatively small amounts of data have to be transmitted. In this case, a number of possible constellations, i.e., possible phase angles in the case of use of a discrete multitone modulation on different carrier frequencies, is reduced, and only those constellations which require a relatively small signal-to-noise ratio are used. It is thereby possible to reduce an output power of an employed line driver and thus save energy.
Such a principle is also applicable to DSL systems other than ADSL, for example, to VDSL systems. In this case, the described method has the disadvantage that only the power consumption for the transmission, i.e., in an analog part, but not the power consumption in digital circuit sections or digital parts of a corresponding transmitting or receiving device, is reduced. Due to the substantially higher data rates in VDSL systems, however, the power consumption in this case is substantially higher in the digital parts than in the case of ADSL systems. Moreover, in principle VDSL systems have a lesser output power than ADSL systems, so that, for this reason also, the power consumption is relatively greater in the digital parts than in the case of ADSL systems.